There is known the introduction of fillers to thermoplastic polymers in order to improve the useful properties but with improved useful properties, the processing properties deteriorate and vice versa.
In the case of polyolefins the improvement of mechanical properties is achieved with great difficulty because of very low physical adhesion and lack of chemical adhesion between the polyolefin and the mineral filler. There are also known methods for improvement of adhesion, relying upon the change of physico-chemical properties of the grains of the filler. The simple method of preparation is to give "acidity" to the filler surface by coating the grains with aluminum or magnesium silicate compounds. See, J. Hodgkin, D. Solomon, J. Macromol. Sci. A8 (3) 635 (1974); D. Solomon - BP 1228538 (1969).
Also, from U.S. Pat. No. 4,186,123 (Kietzman) is known a process for coating fibrous minerals, such as asbestos, used as fillers for polymers.
There is also known a method for surface preparation of the fillers by organotitanates. See, Plast.Tech. 22 (4) 71 (1976), Plast.Tech. 22 (4) 81 (1976). For the fillers provided for the polyolefins, coatings made of triisopropylenoxytitanate are applied in a quantity of 0.5 to 3% w/w of the filler.
Among the most popular organic coating substances may be ranked stearic acid, barium, calcium, sodium stearates and their compositions. See, Plast. Tech. 22 (4) 71 (1976), Plast.Tech. 22 (4) 81 (1976), Rev. Plast. Mod. 223, 8 (1975). The known coating media for mineral fillers are silanes, described in the publication Jap. Plastic Age, Sep.-Oct. 33 (1975), Dow Corning Corp. (8-5-70), US-061505, Union Corp. (5-17-68) US-862027.
Silanes of the general chemical formula R'Si(OR).sub.3 possess two types of functional groups, R' and OR. R' is usually a reactive organic group-amine, vinyl, epoxide, methacrylate, bonded to a silicon atom by short aliphatic chains but OR is a hydrolysable ether group.
Through the OR groups, silanes are bound to the surface of the filler, whereas the functional R' groups react with the polymeric matrix. The known method for preparation of the filler surface is coating with a layer of polymer through polymerization of reactive monomer according to either a radical or a cation mechanism. Monomers such as styrene, pyridine, divinylobenzene, acrylic acid etc. are used. See, Jap. Plastic Age, Sep.-Oct. 33 (1975), J. Macromol. Sci A8 (3) 649 (1974), Asaki Chem. Ind. Co. Ltd. 29 (1967) JA 069210 US Polywood Champion Papers Inc. (8-21-70) US 066107.
Polymer coatings of the molecular weight of 500-800 make up to 3% of the filler weight and their thickness ranges from 20 to 30 .ANG..
The polymer coating may be applied on the surface of the filler in the separate process of preparation or in the presence of the polyolefin during mixing. In this last case, the amount of the catalyzer is used so as to initiate polymerization but not to cause cross-linking of the polyolefin.